Field of the Invention
The present invention relates to a motor and a sensing magnet of the same, and more particularly, to a steering motor and a sensing magnet structure of the same.
Discussion of Related Art
A steering system is a system for ensuring steering stability of a vehicle, and assists steering by separate power.
In recent years, instead of an auxiliary steering device using oil pressure, an electronic power steering (EPS) system which has a little loss of power and is excellent in accuracy has been mainly used. The EPS includes a speed sensor, a torque angle sensor, a torque sensor, and the like.
An electronic control unit (ECU) detects running conditions through sensors included in the EPS, and drives a motor in accordance with the detected running condition. Thus, turning stability is ensured and rapid turning resiliency is provided, thereby enabling safe driving of a driver.
In the EPS system, a motor (hereinafter, referred to as “EPS motor”) assists a torque for operating a handle so that a driver can perform steering operation with less power. As the EPS motor, a brushless direct current (BLDC) motor or the like can be used. The BLDC motor refers to a DC motor in which an electronic commutation mechanism is installed except a mechanical contact unit such as a brush, a commutator, or the like.
The EPS motor includes a sensing magnet for detecting an amount of rotation of the motor for the purpose of steering assistance and a sensor.
The sensing magnet is formed in a disc shape, and includes a main magnet formed on an inner side thereof and a sub magnet formed on an outer circumferential side thereof.
The main magnet includes a plurality of poles arranged in the same manner as magnets inserted into a rotor in an EPS motor, and is disposed so as to face the sensor. The sensor detects a change in magnetic flux in accordance with rotation of the main magnet, and transmits the detected signals to an ECU, thereby enabling the ECU to calculate rotation of the rotor.
The sub magnet includes a larger number of poles than those of the main magnet. The sub magnet disposes a plurality of poles so as to correspond to the single pole of the main magnet. Thus, a rotation angle may be more finely divided to be measured, and therefore driving of the EPS motor may be more smoothly performed.
A dummy track is disposed between the main magnet and the sub magnet for the purpose of minimizing the interference of the magnetic flux between the main magnet and the sub magnet and achieving sequential magnetization of the main magnet and the sub magnet.
As described above, the sensing magnet includes the main magnet and the sub magnet, and therefore an inner ring portion including the main magnet and an outer ring portion including the sub magnet are sequentially magnetized at predetermined intervals. Accordingly, two magnetization processes are performed at predetermined intervals, and therefore there is a problem that a magnetization time is increased.
In addition, the dummy track which is not used exists between the main magnet and the sub magnet, whereby costs of materials are increased.
In addition, non-uniformity of duty of frequency generator (FG) signals which are output from the sensor may occur due to occurrence of the interference of the magnetic flux between the main magnet and the sub magnet, whereby sensing accuracy is deteriorated.